The present invention relates to the synthesis and use of new aluminum compounds as precursors for chemical vapor deposition (CVD) to obtain high-quality aluminum films. More particularly, the present invention relates to new precursors for chemical vapor deposition of aluminum, which are non-pyrophoric and stable in the gas phase at elevated temperatures to maintain their molecular integrity, and use thereof.
Chemical vapor deposition of aluminum films has attracted much attention as conventional deposition techniques such as sputtering are expected to be problematic for processing ultra large scale integration (ULSI) devices in the microelectronics industry. However, CVD method requires organoaluminum precursors which are volatilized and decomposed to produce aluminum films.
Triisobutylaluminum (TIBA) is one of the organoaluminum precursors which has received the most attention among the trialkyl aluminum compounds as CVD precursors because of its ability to deposit high-purity aluminum films (A. Malazgirt et al., Metallugical Transactions B 1980, vol. 11B, 225; M. A. Green et al., Thin Solid Films 1984, vol. 114, 367; and B. E. Bent et al., J. Am. Chem. Soc. 1989, vol. 111, 1634). However, TIBA has a tendency to decompose to the less volatile diisobutylaluminum hydride in the gas phase (K. W. Egger, J. Am. Chem. Soc. 1969, vol. 91, 2867) and gives aluminum films of poor reflective properties (R. A. Levy et al., J. Electrochem. Soc. 1987, vol. 134, 37C). Dimethylaluminum hydride (DMAH) has been reported to be a substantial improvement over TIBA or other alkyl aluminum complexes (R. Bhat et al., J. Cryst. Growth 1986, 77, 7), but a later study showed that the levels of carbon contamination in the Al.sub.x Ga.sub.I-x. As layers deposited from DMAH were identical to those obtained from trimethylaluminum (A. C. Jones et al., J. Cryst. Growth 1990, 100, 395).
Donor-acceptor complexes of alane (AliH.sub.3) such as trihydrido(trialkylamine)aluminum (D. R. Carley et al., U.S. Pat. No., 3,375,129) have been reported to be used for aluminum plating since the late 1960s and have recently attracted much attention as precursors for CVD of aluminum (W. L. Gladfelter et al., Chem. Mater. 1989, 1, 339). These tertiary amine alanes are less air-sensitive than the trialkylaluminums. Since there is no aluminum-carbon bonds in these compounds, carbon incorporation in the deposited films is minimized. A major problem for these complexes is their low thermal stability. Trimethylamine alane (TMAA) has been used as a precursor for CVD of aluminum and demonstrated high growth rates and low growth temperatures. Despite its high stability compared to other amine alane complexes, a disadvantage of TMAA as a practical CVD precursor is that it is a solid with a relatively high melting point. A few alane complexes with bulkier amines, such as triethylamine, diethylmethylamine and dimethylallylamine, are known to be liquids (J. K. Ruff et al., J. Am. Chem. Soc. 1960, 82, 2141). However, the thermal stability of tertiary amine alane complexes decreases as the amine gets bulkier.
Though dimethylethylamine alane (DMEAA) has been reported to be the optimal tertiary amine alane complex since it is a volatile liquid with considerable thermal stability (W. L. Gladfelter et al., U.S. Pat. No. 5,191,099), several problems still remain to be solved. DMEAA dissociates to give free amine, alane, and aluminum during storage as well as during vaporization processes. Excess amine is added to the precursor vessel to avoid the dissociation of the precursor during storage. However, this cannot solve the problems arising from the intrinsically poor vaporization behavior of DMEAA at elevated temperatures originating from its thermal instability. Aluminum particles have been reported to be observed in the gas phase during the CVD process using DMEAA (M. G. Simmonds et al., J. Vac. Sci. Technol. 1991, A9, 2782).